It is heartrending to hear injured children and the relatives of the dead say they do not hate anybody as a result of their terrible experiences and, if they feel anger at all, it is only directed towards the bomber himself. Victims repeatedly say that they did not want the slaughter at the Manchester Arena to be used to create divisions in their city.

The downside of this praiseworthy attitude is that it unintentionally lets off the hook those British authorities whose flawed policies and mistaken actions really did pave the way towards this atrocity. Appeals against divisiveness and emphasis on the courage of survivors have muted attacks on the government, enabling it to accuse those who criticise it of mitigating the sole guilt of Abedi.

This attitude is highly convenient for former prime minister David Cameron who decided in 2011 on military intervention against Muammar Gaddafi. His purported aim was humanitarian concern for the people of Benghazi, but – as a devastatingly critical report by the House of Commons Select Committee on Foreign Affairs said last year – this swiftly turned into “an opportunistic policy of regime change”.

The military intervention succeeded and by the end of the year Gaddafi was dead. Real power in Libya passed to Islamist militias, including those with which the Abedi family were already associated. Pictures show Salman’s brothers posing with guns in their hands. Libya was plunged into an endless civil war and Benghazi, whose people Cameron and former French president Nicolas Sarkozy were so keen to save, is today a sea of ruins. Inevitably, Isis took advantage of the anarchy in Libya to spread its murderous influence.

This is the Libyan reality which was created by Cameron and Sarkozy, with sceptical support from Barack Obama, the then US president, who famously referred to the Libyan debacle as a “shit show”.

Libya became a place where the Abedi family, returning from their long exile in Manchester, were able put their militant Islamist beliefs into practice. They absorbed the toxic variant of Islam espoused by the al-Qaeda clones, taking advantage of their military experience honed in the Iraq war, such as how to construct a bomb studded with pieces of metal designed to tear holes in human flesh. The bomb materials were easily available in countries like Britain.

Salman Abedi was responsible for what he did, but he could not have killed 22 people and maimed another 139 others, half of them children, if the British government had not acted as it did in Libya in 2011. And its responsibility goes well beyond its disastrous policy of joining the Libyan civil war, overthrowing Gaddafi and replacing him with warring tribes and militias.

Manchester had since the 1990s become a centre for a small but dangerous group of exiled Libyans belonging to anti-Gaddafi groups, such as the Libyan Islamic Fighting Group, originally formed by Libyans fighting the communists in Afghanistan. After the invasion of Iraq in 2003, strict measures were taken by MI5 and the police against Libyans thought likely to sympathise with al-Qaeda in Iraq and, later, Isis. They were subject to counter-terrorism control orders monitoring and restricting their movements and often had their passports confiscated.

But no sooner had Britain joined the war against Gaddafi than these suspected terrorists became useful allies. Their control-orders were lifted, their passports returned and they were told that the British government had no problem with them going to Libya to fight against Gaddafi. In place of past restrictions, they were allowed to pass to and fro at British airports. Some militants are reported as saying that when they had problems with counter-terrorism police when flying to Libya, the MI5 officers with whom they were in touch were willing to vouch for them and ease their way to the battlefront in Libya, where MI6 was cooperating with Qatar and UAE as financiers of the armed opposition.

This opportunistic alliance between the British security services and Libyan Salafi-jihadis may explain why Salman Abedi, though by now high up on the list of potential terrorists, was able to fly back to Manchester from Libya unimpeded a few days before he blew himself up.

There should be far more public and media outrage about the British government’s role in the destruction of Libya, especially its tolerance of dangerous Islamists living in Britain to pursue its foreign policy ends. The damaging facts about what happened are now well established thanks to parliamentary scrutiny and journalistic investigation.

The official justification for British military intervention in Libya is that it was to prevent the massacre of civilians in Benghazi by Gaddafi’s advancing forces. The reason for expecting this would happen was a sanguinary speech by Gaddafi which might mean that he intended to kill them all. David Cameron, along with Liam Fox as defence minister at the time and William Hague as foreign secretary, have wisely stuck with this explanation and, as a defence of their actions, they are probably right to do so. But a report by the House of Commons Foreign Affairs Select Committee says that the belief that Gaddafi would “massacre the civilians in Benghazi was not supported by the available evidence”. It points out that he had retaken other towns from the rebels and not attacked the civilian population.

The British followed the French lead in military intervention and Sarkozy similarly justified his policy as being in defence of the people of Benghazi. We are a little better informed about the real French motives thanks to a report, revealed through the Freedom of Information Act, made in early 2011 by Sidney Blumenthal, an unofficial advisor to Hillary Clinton, the then US secretary of state, after a meeting he had had with French intelligence officials about Sarkozy’s motives for intervention.

The officials told Blumenthal that Sarkozy’s plans were driven by five main causes, the first being “a desire to gain a greater share of Libya oil production” and the next being to increase French influence in North Africa. His other aims were to improve his own political standing in France, enable the French military to reassert their position in the world, and prevent Gaddafi supplanting France as the dominant power in Francophone Africa.

The intelligence officials make no mention of any concern on the part of Sarkozy for the safety of the Libyan people. Conceivably Cameron, Hague and Fox had much purer and more altruistic motives than their French counterparts. But it is more likely that the aim was always regime change in the national interest of those foreign powers who brought it about.

It is easy enough to convict Cameron and Sarkozy of hypocrisy, but a more telling accusation is that they betrayed the very national interests that they were seeking to advance. They destroyed Libya as a country, reduced its six million people to misery and played into the hands of men like Salman Abedi.